In LTE(Long Term Evolution) and successor systems of LTE (for example, LTE-A (LTE Advanced), FRA(Future Radio Access), also called 4G or the like), a D2D (Device to Device) technology for user apparatuses (UEs) to carry out communication together directly without using a radio base station (eNB) has been studied (for example, Non-patent Reference No. 1).
D2D enables reduction of traffic between a UE and a eNB, and enables communication between UEs even if a eNB is in a communication impossible state due to a disaster or the like.
D2D is classified roughly into D2D discovery and D2D communication (D2D direct communication). Below, D2D communication and D2D discovery will be simply referred to as D2D if D2D communication and D2D discovery are not particularly distinguished. Also, a signal transmitted and received by D2D will be referred to as a D2D signal.
Also, in 3GPP (3rd Generation Partnership Project), it has been studied to implement V2X by extending the D2D function. As shown in FIG. 1, V2X includes a V2V (Vehicle to Vehicle) meaning a communication mode between an automobile (one example of a vehicle) and an automobile; V2I (Vehicle to Infrastructure) meaning a communication mode between an automobile and a road-side unit (RSU) installed at a road side; V2N (Vehicle to Nomadic device) meaning a communication mode between an automobile and a mobile terminal of a driver; and V2P (Vehicle to Pedestrian) meaning a communication mode between an automobile and a mobile terminal of a pedestrian.